1. Field of the Invention
The present invention relates to filter clogging determination apparatuses for diesel engines, which determine from the estimation of exhaust pressure the clogging of a diesel particulate filter disposed in an exhaust system.
2. Description of the Related Art
Known diesel engines collect particulate matter (PM) from exhaust gas by passing the exhaust gas through a diesel particulate filter (DPF) disposed in an exhaust passage. PM collected in the DPF accumulates as time elapses. If the amount of collected PM is excessive, the filter will clog, producing resistance in filter passages and hence an increase in exhaust pressure in the diesel engine, ultimately causing a decrease in output. To prevent this, the DPF must be regenerated by, for instance, periodically heating and combusting accumulated PM, thereby removing the PM.
Examples of technology for combusting PM include heating the DPF itself. However, overheating of a DPF may result in early deterioration and a decrease in its durability. To avoid this, the following means for removing PM is generally adopted: separately from the regular injection of fuel, fuel is post-injected into a cylinder during an expansion or exhaust stroke after compression, or fuel is supplied immediately in front of the DPF; thereby increasing the temperature of exhaust gas and oxidizing PM.
To regenerate a DPF, exhaust pressure upstream of the DPF or the difference between exhaust pressures before and after the DPF is measured. When the exhaust pressure upstream of the DPF or the difference between the exhaust pressures becomes equal to or greater than a predetermined value, the DPF is regenerated.
For example, Japanese Patent Application Laid-Open No. 2002-21623 discloses technology in which an exhaust pressure sensor for detecting exhaust pressure is disposed at the entrance of the DPF, and exhaust pressure at the entrance of the DPF is monitored to estimate the amount of PM accumulated in the DPF.
Japanese Patent Application Laid-Open No. 2003-97333 discloses technology in which an exhaust sensor for detecting the oxygen concentration of exhaust gas is disposed upstream of a DPF, and exhaust pressure is estimated from the oxygen concentration detected.
However, the technology disclosed in Japanese Patent Application Laid-Open No. 2002-21623 requires an exhaust pressure sensor to be specially installed upstream of the DPF, with the result that the number of components and hence the manufacturing costs increase. Similarly, where a difference between the pressures before and after the DPF is used to estimate an amount of accumulated PM, a pressure difference sensor is required, which also increases the number of components and the manufacturing costs.
The technology disclosed in Japanese Patent Application Laid-Open No. 2003-97333 estimates the amount of accumulated PM from the output voltage of an exhaust sensor. This makes it difficult to determine whether a change in output voltage results from a change in the oxygen concentration of the exhaust gas or from an increase in exhaust pressure.
Further, in the technology disclosed in Japanese Patent Application Laid-Open No. 2003-97333, the target output with which the output voltage of the exhaust sensor is to be compared must be stored in the form of a map for each operating state. Accordingly, an enormous amount of data must be stored in a storage means.
This requires a tremendous amount of time and cost to collect data through experiments and simulations. Furthermore, the capacity of the storage means must be large enough to store the enormous amount of data. This leads to higher manufacturing costs.